Hey Rod,
if this is the case, shouldn’t you have been able to see how far the broken end was still in the collet?
Wow, a lot of imperial to convert. At first sight such numbers say nothing to me (I would have to convert them).
Also I just was called for dinner! On the web, there are a lot of tables for cutting parameters, e.g. this one here that includes brass as material (PDF). Good tables for metal are also in the book ISBN 9783758510717.
What do you think of the cable problem theory? Especially since Onefinity lacks strain relief on their cables and the Molex pin crimps are not strong enough to redeem this fault.